1. Field of the Invention
The present invention relates to an evaporated fuel treatment device, and more particularly to an evaporated fuel treatment device for treating evaporated fuel generated in a fuel tank without emitting it to the atmosphere.
2. Background Art
A conventional evaporated fuel treatment device disclosed, for instance, by JP-A No. 2001-294052 is equipped with a canister that communicates with a fuel tank. This device is also equipped with a sealing valve that is positioned in path between the fuel tank and canister. The sealing valve opens for refueling and in other situations where evaporated fuel should be allowed to escape from the fuel tank. In such an instance, the canister absorbs the evaporated fuel escaping from the fuel tank. When predefined purge conditions are established, the evaporated fuel absorbed by the canister is purged into an internal-combustion engine's intake path. As a result, the evaporated fuel generated in the fuel tank is treated as fuel without being emitted to the atmosphere.
The above conventional device is capable of checking for leakage in the device by the method described below. After internal-combustion engine startup, the device first detects the tank internal pressure while the sealing valve is closed. If the detected tank internal pressure is close to the atmospheric pressure, the device opens the sealing valve to conduct a leak check on the whole line containing both the fuel tank and canister. If, on the other hand, the tank internal pressure detected with the sealing valve closed is a predetermined positive pressure or negative pressure, the device immediately makes a judgment that no leakage is in the fuel tank. Then, a check is made for determining whether leakage is in the line on the canister side with the sealing valve left closed. The use of the above method makes it possible to detect leakage in the device accurately and promptly after internal-combustion engine startup.
However, the above conventional device does not take sealing valve failure diagnostics into consideration. If an open failure occurs in the sealing valve, a desired evaporated fuel treatment capacity may not be obtained due to an improperly closed fuel tank. If a close failure occurs in the sealing valve, a desired refueling characteristic may not be obtained. Therefore, when the employed system is equipped with a sealing valve that hermetically closes the fuel tank, it is desirable that a failure diagnostic check be accurately conducted on the sealing valve.